Not sure if right area of the site to post this but very desperate to find solution! Since 2018 have had the DTC of PO420 in my 2013 F-150. My dealership I use has spent several months diagnosing this issue. Every component used for the converters to operate correctly has been diagnosed and replaced at least 3 times. The PCM, Upstream and downstream cats, upstream and downstream O2 sensors, all wiring harnesses have been checked and OK'd to be good and no problems detected. This F-150 has been in the shop twice first time for approximately 3 weeks then released to me, where I drove with DTC PO420 still coming on. I would record details when engine light would come on and what conditions to my ability. I have now retuned the F-150 back to the dealership where it has been since March 6, 2023. Yes 3 months!!! As stated previously in this post every component I know of dealing with the converter system of this truck has now been replaced from the PCM to the downstream O2 sensor, at least 3 times and some such as the converters 4 times and the tech now is planning to replace the converts again. I don't know what diagnostic procedures were preformed but my opinion is that they were not effective at all. As a wild guess it had been mentioned to me to checking the throttle position sensor. Would that effect this issue? Like to hear some responses please! I have made contact with Ford Customer Support in this matter for help and they are responding but thought I would ask here also. If need be e-mail me at speadtrap@bellsouth.net Thanks Folks.